Global death toll from Covid-19 crossed 5 million on November 1, 2021. While this is based on official figures reported by different countries, the actual number is likely to be much higher, as variably estimated by public health experts. Dips in global case numbers of infection, optimistically reported by the World Health Organisation till recently, have been replaced by upward spike in cases and deaths in its last weekly report of October 28, 2021. This brings home the message that there is no final exit in sight for the SARS-CoV-2 virus.
A widely prevalent expectation that vaccines would quickly terminate the pandemic was based on the false premise that they would completely curtail person to person transmission and would protect a fully-vaccinated person from any infection by the virus. Both these assumptions were inaccurate to begin with and have been proved incorrect by emerging global evidence. Reports of fresh infections in highly vaccinated populations (like Vermont in USA) and the drive for administering third dose boosters to all persons above 12 years of age in Israel have punctured the belief that vaccines fully insulate people against entry of the virus into their bodies.
Persons vaccinated with the currently approved injectable vaccines produce a systemic immune response that combats the virus when it enters their respiratory tract but does not altogether block it from infecting them. Antibodies that are produced by the B lymphocytes (IgM and IgG) will fight the virus in the blood stream, while the T lymphocytes will attack the virus after it has entered the human cells. Mucosal vaccines, which can copiously generate secretory antibodies (IgA) that can wash away the virus from the lining of the respiratory tract, are still to emerge from the clinical trial pathway.
Fully vaccinated persons can be infected by the virus and others who acquired immunity from a natural infection can be reinfected. In both cases, the infection is mostly mild as the previously acquired immunity offers a high level of protection against severe disease, hospitalisation and death. Such persons may not get very sick or even remain asymptomatic but can discharge virus particles into the air which others breathe. Indeed, recent evidence suggests that the viral load in the respiratory tract of a vaccinated person is the same as that in an unvaccinated person, when infected by the virus. However, a person with mild illness is unlikely to discharge many virus particles and not for long, when compared to a severely ill person. So, vaccines will reduce transmission to some extent but not eliminate that risk altogether.
We can more effectively reduce transmission risk by preventing discharge of the virus into the air around us, by wearing proper face masks the proper way. We can reduce the likelihood of exposing our respiratory tract to a high viral fusillade by avoiding crowded areas and moving or working in well ventilated spaces. A combination of these measures and full vaccination, if practiced by all persons in a community, can greatly reduce the risk of new infections and prevent severe illness. Some infections may still occur as neither of these strategies is 100% effective in preventing viral transmission. Our aim must be to greatly reduce transmission in the community and prevent severe disease in the persons who are infected.
It is not easy to completely exorcise any virus from the world. It is especially difficult to do so for respiratory viruses. The only viruses which have been eradicated so far are small pox in humans and rinderpest in cattle. Despite widespread global success in the polio eradication campaign, cases are still occurring due to the wild virus in two countries and vaccine derived viruses in a few others. Respiratory viruses are especially likely to stay on amidst us, even if they grow milder with time. Nobel Laureate Joshua Lederberg, who opened our understanding of microbial genetics, wrote that it is unrealistic to think of eradicating most microbes and opined that it is a bout between “our wits and their genes.” We will have to learn to live with many viruses amidst us, not as a compromise forced on us by their power to change shape but as a negotiated settlement that science helps us to achieve by containing their virulence.
So, how do we make the Covid virus milder, even if we can’t get fully rid of it? By using the drivers of evolutionary biology to change virus behaviour. Viruses, which are tiny particles that are not truly alive in the conventional sense but depend on animal or plant life for their replication and species continuity, can evolve far faster than the much larger humans do. Since their aim is to continue their species, they prioritise mutations that enhance their infectivity when the host population is not easily accessible. They will trade such increased transmissibility for reduced virulence since they cannot afford to extinguish their host population. Even if the human population is large, we can reduce the numbers who are susceptible to the virus by our public health measures and personal behaviours. By restricting their access to susceptible humans, we can steer virus evolution towards lower virulence.
Such a change to lower virulence has happened to other viruses. The H1N1 virus was much more virulent in the last century than its descendant which caused only a mild flutter in 2009. So, the ability to change the behaviour of the virus is linked to our behaviour. If we recklessly expose large numbers of the human population to the virus through super-spreader events, there will be no incentive for the virus to become less virulent. By creating evolutionary pressure on the virus by limiting its access to unprotected humans, we can change its form and nature.
We will have to reach that equilibrium point of coexistence, even as we develop better vaccines and drugs. We need those technologies but without human behaviour change, we will still have an Achilles’ heel exposed to the virus. In this complex adaptive system, equilibrium points may periodically change as the virus throws up new variants and we come up with new scientific knowledge and technologies to counter. At the same time, we have to resume our economic and social activities as a functioning society, both at national and global levels. So, our behaviour has to be calibrated to secure a steady and safe return to normalcy. That will require large sections of the global population to be vaccinated, through sharing of vaccine stocks and production technologies as well as greater discipline in avoiding large crowded events till the virus is tamed. If there is an outbreak anywhere, even after the pandemic has waned, a quick containment strategy has to be implemented. Masks are likely to be needed for some months more. Even when the danger seems past, persons with respiratory infections may need to wear them when unwell, as is customary in East and South East Asian countries.
As we contemplate the future and hope that greater global solidarity will be a legacy of this pandemic, we should also work to reduce the risk of future zoonotic pandemics. Curtailing and reversing deforestation would be a good measure, as the wanton destruction of forests builds conveyor belts for viruses to travel from forest dwelling wildlife to large human populations by removing nature’s protective barriers. Changing to predominantly plant based diets, from those packed with meat, will also help to curtail viral transmission while reducing the drive for deforestation related to animal breeding. Will we act wisely? While the virus is guided solely by evolutionary biology focused on species survival, we are increasingly driven by commercial interests and political preoccupations that lead public policy and personal behaviours astray. Can we learn from the virus, to behave smartly, even as we accept that we have to live with it?
The writer, a cardiologist and epidemiologist, is President, Public Health Foundation of India (PHFI). The views expressed in this article are those of the author and do not represent the stand of this publication.